This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Drug-induced liver injury is a major safety issue in anti-tuberculosis chemotherapy. The objective of this project is to investigate the mechanisms of liver injury associated with rifampicin and isoniazid co-therapy and to develop novel strategies to manage rifampicin and isoniazid induced liver injury. By using pregnane X receptor (PXR)-humanized mice, our preliminary studies identified that human PXR is essential in rifampicin and isoniazid induced liver injury. Our central hypothesis is that rifampicin-mediated human PXR activation disturbs the metabolism of isoniazid and bile acids, and these metabolic disorders result in the liver injury caused by rifampicin and isoniazid co-therapy. In order to test our hypothesis, we will utilize the genetically engineered mouse models (Pxr-null, PXR-humanized, and Cyp3a-null mice) and the LC-MS-based metabolomic approach to pursue the following specific aims: (1). Determine the importance of Cyp3a in rifampicin and isoniazid induced liver injury. (2). Define the effects of rifampicin-mediated PXR activation on isoniazid metabolism and disposition, and determine the mechanism of rifampicin-boosted isoniazid toxicity. (3). Define the effect of rifampicin and isoniazid co-treatment on bile acid metabolism, and determine its contribution in rifampicin and isoniazid induced cholestatic injury. This work is innovative in that human PXR is identified as an essential mediator of rifampicin and isoniazid induced liver injury. Successful completion of this project will greatly enhance our knowledge on rifampicin and isoniazid induced liver injury which will be applied towards predicting, preventing, and treating the liver injury caused by rifampicin and isoniazid co-therapy.